As a general rule, a communication system strives to conserve the overall bandwidth that is available to it. As a given bandwidth is used more efficiently, a greater quantity of information may be communicated using given communication resources.
Real time human speech represents one type of information that is often delivered through a communication system. Human speech contains a large quantity of silent periods. To a large extent, for a conversation to be successful one party to the conversation must be silent when another party to the conversation is talking. Moreover, even when one party is talking, the talking party's speech is permeated with small periods of silence. Accordingly, a technique known as digital speech interpolation (DSI) may be used to efficiently utilize a bandwidth that is available for the transmission of many independent conversations. Generally speaking, DSI divides speech from many conversations into frames of relatively short time spans. On a frame-by-frame basis, the available resources are allocated to only those conversations which are not silent. As a general rule, up to a 50% improvement in overall bandwidth utilization results from not transmitting the silent periods in human speech.
On the other hand, a transceiver which operates within a DSI scheme must be extremely agile in its ability to switch between various channels that are available within the overall communication system bandwidth. A previously used channel becomes unavailable to a given conversation after a silent period because the communication system assigns the previously used channel to another conversation at the instant silence begins. The communication system identifies and assigns available channels at the instant silence ends. In order to prevent the loss of information, a transceiver needs to quickly switch to a newly assigned channel.
Data generated by and communicated between computerized devices represent another type of information that is often delivered through communication systems. These data often need not be delivered in real time. In other words, the data may be transmitted at any rate consistent with the available system bandwidth. Communication systems often force such data to be transmitted through a constant bandwidth channel which might otherwise be suitable for real time data. This represents an inefficient use of an overall communication system bandwidth which has a multiplicity of channels. Channels often go unused on an instant-by-instant basis when the communication system is operating at less than its maximum capacity. Any period of time over which a channel remains unused represents an inefficiency which could be improved upon. Data which need not be delivered through a constant bandwidth channel could be transmitted over otherwise temporarily unused channels. Overall bandwidth usage efficiency would improve due to increased data transmission rates. However, a transceiver which is compatible with a variable bandwidth data transmission scheme would need to quickly switch to newly assigned channels on an instant-by-instant basis as such channels become available.
When communication systems employ frequency division multiple access (FDMA) transmission schemes, transceivers operating in accordance with DSI and/or variable bandwidth transmission techniques would need to quickly switch their operation between different frequency channels. In these situations, a transceiver needs to modify its operation and be capable of communicating through a new frequency channel within a period of time equivalent to an inter-frame or inter-timeslot timing gap to prevent the loss of information. In most communication schemes, such timing gaps are as short as possible, often on the order of a few tens of microseconds, because no communication can occur during these gaps and shorter gaps improve overall efficiency.
Unfortunately, frequency synthesizers which are capable of quickly and accurately slewing to and/or locking onto new frequencies over a range of many different frequency channels are extremely expensive. Such synthesizers may be constructed substantially from discrete components or from integrated circuits which undergo an unusually high level of processing and testing. Either way, such synthesizers may cost many times what synthesizers having a more moderate frequency locking rate cost.
Moreover, transceivers which include such high frequency locking rate synthesizers often suffer from reduced reliability. Locking rate becomes a critical parameter for successful transceiver operation. The locking rate describes the amount of time required for a synthesizer to slew its frequency output from an old frequency to a new frequency and become locked at the new frequency. Any deterioration over time in this locking rate parameter can directly and adversely affect transceiver operation.